Steps to reproduce:

  With some kind of image tarball bookworm.tar

    $ autopkgtest-virt-unshare -t bookworm.tar
    ok
    open
    ok /tmp/autopkgtest.HYR0W4
    print-execute-command

  Then in another terminal, using that command with the commas
  replaced with spaces:

    $ unshare --map-auto --map-root-user --user --mount -- /usr/share/autopkgtest/lib/unshare-helper /tmp/tmp_8rqn1g5 -- sleep 12345

  Observe with ps -efH | grep sleep that the sleep 12345 is running.

  Now, in the autopkgtest-virt-unshare terminal,

    close

Expected behaviour:

  The sleep is killed.  The unshare rune exits.
  Then "ok" from autopkgtest-virt-unshare

Actual behaviour

  "ok" from autopkgtest-virt-unshare.
  But, the sleep and the unshare rune are still running.